Process for separating olefinic hydrocarbons using silver fluoborate and silver fluosilicate solutions



Unite p 2,913,505 PROCESS FOR SEPARATING OLEFINIC HYDRO- CARBONS USING SILVER FLUOBORATE AND SILVER FLUOSILICATE SOLUTIONS Hans Geor Van Raay, Dusseldorf, and Ulrich Schwenk, Frankfurt am Main, Germahy, assignors to Farbwerke ,;Hoechst'Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany Application May 14, 1957, Serial No. 659,055 Claims priority, application Germany May 27, 1956 i 10 Claims. (c1. 260-677) The present invention relates to a process for separating olefinic hydrocarbons.

It is already known that olefins and substituted olefins form complex compoundswith heavy metal salts by an addition reaction with the metal ions (for example Pt, Ag, Cu(I) or Hg(II) ions). Of these salts the Ag, Cu(I) and Hg(II) salts are of particular technical intere'st for the separation of olefins or substituted olefins from mixtures with other hydrocarbons or their substitution products.

Contrary to cuprous salts, mercury salts silver salts pecially when in view of the'improved space/time-yield' the advantage of a high solubility of the olefin in the silver solution outweighsth'e disadvantage of the higher cost of the silver. Numerous processes for separating olefins by means of aqueous solutions of the nitrates, chlorides, acetates or sulfates of the above mentioned three metals (Ag, Cu(I), Hg(II)) are described in literature. In many cases monoor polyhydric alcohols, amines, hydroxylamines, cyclic amines, cyclic ethers, nitriles etc. are added. The addition of such dissolving intermediaries generally also leads to an improved solubility of the non-olefins and thus impairs the separating effect. The solubility of the olefins is substantially determined by the concentration of the metal ions, an increase in the metal content of the solutions being associated with a strong increase in solubility. The same. efiect is obtained by pressure increase; it is, however, more convenient to work under atmospheric pressure or slight superatmospheric pressure. v

Now we have found that highly concentrated aqueous solutions of silver fiuoborate, silver fluosilicate or combinations thereof, have a dissolving power for olefinic hydrocarbons that is superior to that of aqueous silver nitrate solutions. For example, such solutions may contain up to above one kilogram of silver per liter of purely aqueous solution (that is, for example, four times the concentration of a silver nitrate solution saturated at room temperature), and as anion fiuoborate or fluosilicate ions or combinations thereof. The dissolving power for olefins of these solutions is about ten times higher than that of the best cuprous salt solutions of which, for example, Hagen-Haubers cuprous 1 nitrate solution in aqueous ethanolamine dissolves at room temperature about 30-35 liters of ethylene per liter of solution. 1 liter of an indusln contradistinction thereto, the.

In view of these facts it appears adtates Patent 2,913,505 Patented Nov. 17, 1959 from the solution by boiling.

oxide- (above 10% The present invention provides a process for separating olefinic hydrocarbonsfrom hydrocarbon mixtures containing said olefins, which comprises contacting said hydrocarbon mixtures with an aqueous solution of a compoundcontaining silver and fluorine, i.e. silver 1 fiuoborates and/0r silver fluosilicates or mixtures thereof.

The present process is especially suitable for the separation of fluid olefins from fluid hydrocarbon mixtures, the term fluid being understood in both cases to mean gaseous or liquid.

The process of the invention can be carried out in a simple circulation apparatus for the continuous separation of olefins from hydrocarbon gases.

An apparatus suitable for usein carrying out the process of this invention is illustrated diagrammatically in the accompanying drawing:

Referring to the drawing, the-gas to be used enters the apparatus at 1. In the absorption column 2 it meets the concentrated solution of AgBF and/or silver fluosilicate flowing in counterc urrent and is brought into intensive contact with said solution and all the olefin is washed out except for avery small rest so that the gases neednot be recycled. The residual gas leaves thecolumn at 3. The solution charged with the olefins proceeds through a flow-measuringdevice 4 (for example a rotameter) and a preheatingcoil g to stripper 7 provided with a heating jacket 6, inpwhi'ch stripper nearly all the olefin is set free by heating-iorijdis'tillation of the solution. The olefin then travels viaicoolerifijito lye washer 9 where any acid vapors possiblyg fentraine'd are washed out so that acurrent of neutral purityof considerablyabov v 10. The lye. is lIECYClCd'bY meansof Pump. 11. I The silver, fiuoborate solutionfwhich filter 14 andreturned ir'itov the absorptioncolumn by pump 15. Reservoirs for the silver solutionand for the lye as Well as further fittings are not shown the drawing. The above described apparatusenablesspace/time yields of about liters of olefin gas per'liter of absorption space and hour to be obtained. With appropriate constructional modifications and after arrangement of an additional pump 16, the apparatus may of coursealso be used for the liquid extraction of olefin-containing hydrocarbon mixtures (for example benzines obtained by synthesis or from cracking) and-subsequent distillation of the olefin-containing silver solution." q r The gas tobeused the process of the invention may also contain carbon dioxide, carbon hydrogen, nitrogen or noble gas. found that a contempt acetylene o in the form of small dark'parti cles together with small amounts of'silver and may be continuously removed from said .solutionlby means ;of'.the"filter.-'14. "Acetylene V time give rise tothe separationof relatively large amounts of silver acetyissuitable previ-j' ously to hydrogenate selectively the acetylene to yield ethylene. gHigh'er initialconcentrationsof-carbon mon necessitate a high. absorption column concentrations of above 1% after some lide which may cause disturbances. It

e u sa avi ga degree of, e 99% leaves the washer at h i has beentreed from the olefin in the stripperwith addition of "a small amount] of vapor (for promoting the'stripping and replacing about' has been evaporated) monoxide, oxygen, a ur her bee at most, 1% doesnot interfere with the process of the invention; it is bound as silver acetylide which remains suspended in the solution of high separating efiiciency and further require a reduced apparatus charge since CO also shows a certain liability to form complex compounds with silver ions. Contrary to cuprous salt solutions, silver solutions of the aforesaid kind show a considerably smaller stability of linkage for C than for olefins so that in this case, too, separation can be effected when proceeding cautiously. Even in the case of an initial concentration of above 30% of CO, the content of carbon monoxide in the final product !can be decreased to about 4%, for example, with a maximum charge even after one throughput.

The other aforesaid gases, added in any desired initial concentration, are in each case separated quantitatively; their concentration in the olefinic product is in most cases below 0. 1%.

The following examples serve to illustrate the invention but they are not intended to limit it thereto.

Example 1 A silver fluoborate solution containing, per liter, about 800 grams of silver was recycled at a velocity of about 1.5 liters per hour, while the apparatus was charged with industrial ethylene of the following analysis:

CQHQ 0.5% co 3.0% CgHs Rest cgHz, 02, N

(there was no CO present since this had been removed by previous washing with alkali).

The space/time yield amounted to about 100 grams of ethylene per liter of absorption space and hour. 99.8% of the ethylene used was obtained with the aforesaid purity of 99.9%.

Example 2 With the use of an industrial mixture of crude ethane and crude ethylene of the following composition:

48.8% Cal-I Rest H2, N2, 02, traces Of CZHZ and At a velocity of about 50 liters per hour and while otherwise proceeding as described in Example 1, a current of pure ethylene of about 22 liters per hour and a current of waste gas of about 28 liters per hour were obtained. Ethylene content of the product:

Pure ethylene: 99.9% C H, Waste gas: Between 4 and 7% C H Space/time yield: about 45 grams of C H per liter of absorption space and hour; about 90 of the ethylene contained in the gas charged was obtained in a very pure state.

Example 3 The apparatus was provided with a column 4 meters high and filled with Raschig rings. With the use of a silver fluoborate solution of 600 grams of silver per liter at a circulation velocity of 4 liters per hour, there were obtained per hour, 180 liters of pure ethylene (99.4% C H 0.6% CO) from a gas containing 30% of ethylene, 10% of methane, 50% of hydrogen and 10% of CO. The waste gas still contained 1% of ethylene and 14% of CO. By returning part of the pure ethylene into the lower part of the column, the CO content of the ethylene could be reduced to less than 0.3%

Example 4 Example 5 200 cc. of a silver fluoborate solution containing, per liter, 600 grams of silver were shaken at 20 C. with 150 grams of a mixture of liquid propane and propylene in a ratio of 63:37%. In the silver solution 40 grams of propylene of 99% strength dissolved which could be obtained by expansion and boiling at 100 C. In the supernatant liquefied gas phase remained 110 grams of propane/ propylene having a propylene content of 15%.

Example 6 Solubility of olefins in various metal salt solutions: A silver fluoborate solution containing, per liter of solution,

. 1200 grams of silver absorbs at 1 atmosphere absolute and 20 C. 350 liters of ethylene or 400 liters of propylene, whereas a Hagen-Haubers cuprous solution absorbs at 20 C. and 1 atmosphere absolute only 25 liters of ethylene or 5 liters of propylene.

A silver fluoborate solution containing, per liter, 600 grams of silver, absorbs at 20 C. and 1 atmosphere absolute: 110 liters of ethylene, 140 liters of propylene, 100 liters of butylene, 155 liters of butadiene or less than 1 liter of carbon monoxide. A silver fluosilicate solution containing, per liter, 600 grams of silver absorbs 50 liters of ethylene.

We claim:

1. A process for separating a fluid olefinic hydrocarbon from a fluid hydrocarbon mixture containing said olefin which comprises bringing said hydrocarbon mixture into contact with an aqueous solution of a member selected from the group consisting of silver fluoborate, silver fluosilicate and a mixture thereof.

2. A process as defined in claim 1 wherein the initial hydrocarbon mixture contains at most about 1% acetyone.

3. A process as defined in claim 1 wherein the initial hydrocarbon mixture contains in addition a permanent gas other than hydrocarbon.

4. A process as defined in claim 3 wherein the permanent gas is carbon dioxide.

5. A process as defined in claim 1 wherein the initial hydrocarbon mixture is brought into contact with a con centrated aqueous solution of a member selected from the group consisting of silver fluoborate, silver fluosilicate and a mixture thereof.

6. A process as defined in claim 1 wherein the aqueous solution brought into contact with the hydrocarbon mixture is subsequently heated for liberation of the olefin absorbed therein.

7. A process as defined in claim 1 wherein water is added to the aqueous solution after the solution is heated for liberation of the olefin absorbed therein, the amount of water added being about equal to the amount of water evaporated in the heating step, and the solution is recycled for further use in the separation process.

8. A process for separating a fluid olefinic hydrocarbon from a fluid hydrocarbon mixture containing said olefin which comprises bringing said hydrocarbon mixture into contact with an aqueous solution essentially containing silver fluoborate and thereafter heating said solution for liberating the olefin absorbed therein.

9. A process for separating ethylene from a gaseous an aqueous solution of amember selected from the group hydrocarbon mixture containing ethylene which comconsisting of silver fluoborate, silver fluosilicate and a pn'ses bringing said hydrocarbon mixture into contact mixture thereof.

with an aqueous solution of a member selected from the group consisting of silver fluoborate, silver fluosilicate nces C ted in he file Of this patent 5 and a mixture thereof.

10. A process for separating propylene from a gaseous UNIT STATES PATENTS hydrocarbon mixture containing propylene which com- 2,391,404 Friedman et a1. Dec. 25, 1945 prises bringing said hydrocarbon mixture into contact with 2,458,067 Friedman et a1. J an. 4, 1949 

1. A PROCESS FOR SEPARATING A FLUID OLEFINIC HYDROCARBON FROM A FLUID HYDROCARBON MIXTURE CONTAINING SAID OLEFIN WHICH COMPRISES BRINGING SAID HYDROCARBON MIXTURES INTO CONTACT WITH AN AQUEOUS SOLUTION OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF SILVER FLUOBORATE, SILVER FLUOSILICATE AND A MIXTURE THEREOF. 